Many small towns have several
mini- or small roundabouts and over quite a
period of time, I introduced several in
Wokingham, Berkshire (UK) and I am aware of many
other towns that have networks of roundabouts.

But first let's look at
mini-roundabouts that are quite close together:

The
double mini-roundabout

These are
now very familiar and they have been in use since
the first one was installed at Upton Cross,
Dorset in 1970. Where the junction is a
crossroads with straight axes on both arms the
layout will rely on the central dividing island
and the position of the two (raised)
mini-roundabout centres to cause sufficient
deflection for "ahead" traffic. Care
must be taken, whatever the configuration, that
all crossing streams are subject to 60m radius
maximum unless vertical deflections provide
adequate speed control.

A double mini-roundabout now
operating
successfully in Londonderry. Both axes
line up and care was needed to ensure adequate
deflection was provided.

The Ring
Junction

First
installed at a four-arm roundabout crossroads at
Colchester in 1972, the ring junction has seen
limited service; but the principles that it
espoused have been taken much further in larger
networks using roundabouts of any size.

A possible problem with Ring
junctions lies in their potential for locking.
The one at Swindon used to lock up in the early
days because one arm of the five-way junction
carried relatively little traffic. The flow that
circulated around the outside network was often
less than that which tried to turn right and
internal locking occurred; once some drivers
learnt to take the longer clockwise route to
their exit the system locked less.

At Swindon, one of the arms
carried relatively little flow.
Here it is arm 1; as a result flows across arms 2
& 5 are low.
Traffic from these arms tends therefore to enter
the system too
freely and this can, and did, cause lock-up
internally.

Don't be put off ring junctions
though - this was a minor issue that needed
watching. The scheme at Hemel Hempstead -
originally 6-way was very successful.

Links to some satellite
views of Ring junctions from the PixPlot
roundabout databaseThese open in a new window...

I am very excited by the prospect
of getting more schemes under way rather like
Shenley Road, Borehamwood. This shows enormous
potential yet to be realised. Once installed
ongoing costs relate to maintenance of the road
structure and surfacing - very little electrical
work is needed when compared with traffic
signals. Borehamwood shows the way forward for
many towns and villages in the Uk and abroad.

Town networks

Near me in Devon the development
of the town of Newton Abbot was planned as a
roundabout town but has recently been spoiled by
the addition of a second set of traffic signals
at a main junction. It seems that Devon CC may
have decided that pedestrian facilities are best
provided by signals. I shall be watching
developments and noting pedestrian delays at the
new/revised installations. It is already very obvious that
pedestrians will not wait at the signals when displaying the red
man.